Increasing Damping Properties of Helicopter Composite Substructures using Flax Fiber Hybridization

Helicopter structures are heavily influenced by vibrations, which frequently trigger structural changes in later stages of development. While structural dynamics simulations may not be reliable enough, flight testing is often the only way to determine dynamic interactions and excitation. This is especially true for innovative designs, such as eVTOLs, which lack practical experience. One possible solution to minimize design risks is to increase the damping in the vehicle's structure, for which natural fibers offer a promising approach. To this end, this study investigated the hybridization of conventional composites with flax fibers at the substructure level. First, the effect of introducing local flax reinforcements is investigated. Second, the hybridization of double-T beams as classical aerospace structures is investigated. Finally, the effect of hybridization on airfoil structures is tested. The frequency dependent dynamic properties of the structures, damping and stiffness, are measured using experimental modal analysis. Local flax rib reinforcements on shells showed a significant increase in stiffness-damping factor but did not improve damping in flax laminates. According to the investigation, hybridization of conventional composites can lead to a significant increase in damping for both, double-T beams and airfoils. The damping can be increased by three to four times, and there can be a significant improvement in the damping-to-stiffness factor. When analyzing airfoil structures, it has been found that hybridization can substantially improve damping while maintaining sufficient stiffness.